An LCD has the advantages of portability, low power consumption, and low radiation, and has been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras and the like. Furthermore, the LCD is considered by many to have the potential to completely replace cathode ray tube (CRT) monitors and televisions.
A typical LCD usually includes an LCD panel, a gate driver for scanning the LCD panel, a timing control circuit for transmitting image data to the data driver, and a data driver for providing gradation voltages to the LCD panel according to the received image data. The LCD panel includes a color filter substrate, a thin film transistor (TFT) array substrate, and a liquid crystal layer sandwiched between the two substrates. When the LCD works, an electric field is applied to the liquid crystal molecules of the liquid crystal layer. At least some of the liquid crystal molecules change their orientations, whereby the liquid crystal layer provides anisotropic transmittance of light therethrough. Thus the amount of the light penetrating the color filter substrate is adjusted by controlling the strength of the electric field. In this way, desired pixel colors are obtained at the color filter substrate, and the arrayed combination of the pixel colors provides an image viewed on a display screen of the LCD.
If motion picture display is conducted on the LCD, problems of poor image quality may occur. For example, the residual image phenomenon may occur because a response speed of the liquid crystal molecules is too slow. In particular, when a gradation variation occurs, the liquid crystal molecules are unable to track the gradation variation within a single frame period and produce a cumulative response during several frame periods. Consequently, considerable research is being conducted with a view to developing various high-speed response liquid crystal materials as a way of overcoming this problem.
Further, the aforementioned problems such as the residual image phenomenon are not caused solely by the response speed of the liquid crystal molecules. For example, when the displayed image is changed in each frame period to display the motion picture, the displayed image of one frame period remains in a viewer's eyes as an afterimage, and this afterimage overlaps with the viewer's perception of the displayed image of the next frame period. This means that from the viewpoint of a user, the image quality of the displayed image is impaired.
In order to overcome this problem, a residual image reducing mode driving method for the LCD has been developed. The residual image reducing driving method includes the following steps: dividing a frame into a first sub-frame and a second sub-frame; a data driver providing gradation voltages corresponding to normal image data to an LCD panel in the first sub-frame; and after about a half of the frame has elapsed, the data driver providing black-inserting voltages corresponding to black image data to the LCD panel in the second sub-frame.
Accordingly, a viewer perceives the black image during the second sub-frame, and an afterimage of the normal image displayed in the first sub-frame is lost from the viewer's perception during the second sub-frame. This means that there is no overlap of an afterimage with a perceived image of the next frame. Thus from the viewpoint of a user, the image quality of the displayed image is clear.
However, when the LCD works in the residual image reducing mode, the timing controlling circuit needs to work at double a normal frequency so as to transmit both the normal image data and the additional black image data to the data driver.
FIG. 3 shows a typical timing control circuit used in an LCD that works in a normal driving mode. The timing control circuit 11 includes two low voltage differential signaling (LVDS) input terminals communicating with an external circuit of the LCD for receiving image data, and two reduced swing differential signaling (RSDS) output terminals for transmitting the image data to a data driver of the LCD.
When the LCD works in the normal driving mode, if a data-transmitting rate of the timing control circuit 11 is equal to “D” pixel/sec, a working frequency “Xnormal” of the two RSDS output terminals of the timing control circuit 11 is calculated according to the following first formula (1):
                              X                      (            normal            )                          =                              D            Port_number                    =                                    D              2                        <            S                                              (        1        )            The “Port_number” represents the number of RSDS output terminals of the timing control circuit 11. “S” represents an endurable frequency (maximum normal working frequency) of the data driver that communicates with the timing control circuit 11.
FIG. 4 shows the timing control circuit 11 used in an LCD that works in the residual image reducing mode. When the LCD works in the residual image reducing mode, the LVDS input terminals of the timing control circuit 11 need to receive additional black image data. If the amount of additional black image data is equal to the amount of normal image data, and the amount of the normal image data and additional black image data that the timing control circuit 11 needs transmit in one second is equal to “2D”, the working frequency of the two RSDS output terminals of the timing control circuit 11 is calculated according to the following second formula (2):
                              X                      (                          black              -              inserting                        )                          =                                            2              ⁢                                                          ⁢              D                        Port_number                    =                                                    2                ⁢                                                                  ⁢                D                            2                        ≧            S                                              (        2        )            
As shown in formula (2), when the LCD works in the residual image reducing mode, the working frequency “Xblack-inserting” of the timing control circuit 11 goes beyond the endurable frequency of the data driver. However, the data driver does not operate properly in a double frequency working condition. Therefore, the LCD needs one or more additional data drivers to deal with the additional black image data. Thus the cost of the LCD is increased.
What is needed, therefore, is an LCD that can overcome the above-described deficiencies.